Origin and Distribution:

Common yarrow emigrated from Europe to North America where it formed a highly variable interbreeding complex with related native and introduced Asian species. The plant has a worldwide distribution including all of the northern and parts of the southern hemispheres. Common yarrow is naturalized all over Ohio. The plant establishes in a variety of places such as landscapes, pastures, prairies, rocky shores, roadsides, waste areas, and field edges. It thrives in most climates, prefers dry soil, and even tolerates drought. Common yarrow typically establishes in thin soils where conditions are unfavorable for other plants. The presence of the plant in pastures is generally regarded as a sign of deteriorating soil quality.

Plant Description:

Identifiable features of this perennial weed are its creeping rhizomes, finely-divided fern-like foliage, flat-topped clusters of small whitish flowers, and sage-like aroma. Most leaves form at the base of the plant resulting in what appears like a rosette. Emerging later in the season are erect leafy stems tipped with clusters of 1/4-inch-wide flower heads, each consisting of 5 ray flowers surrounding 10 to 30 disk flowers. Plants reproduce by seeds and small patches develop from new shoots emerging from rhizomes (horizontal underground stems).

Root System:

Making up the extensive root system are fibrous roots that extend deep into the soil and much-branched rhizomes (horizontal underground stems) spreading horizontally.

Seedlings and Shoots:

Young leaves are divided into lacey lobes with hairs scattered over the upper surface, lower surface, and edge. Initially, plants produce leaves in a basal rosette. Young plants have aromatic foliage that smells like sage when bruised.

Stems:

Stems are approximately 2 feet tall and either unbranched or forked above. Some plants produce hairy stems while those of others are smooth. Several stems often arise from the same root crown.

Leaves:

Leaves are alternate (1 leaf per node), 3 to 10 inches long, lance-shaped in outline, with highly dissected segments that appear fern-like or feathery, gray-green, and covered with wooly hairs. Basal leaves are numerous and attached to the stem by way of stalks (petioles). Lacking petioles, stem leaves attach directly to the stem. Size decreases as the position of the leaf moves upward toward the tip of the stem. Leaves have a sage-like aroma.

Flowers:

Each flower head is 1/4 inch wide and consists of 5 white or pinkish ray flowers (often mistaken for petals) surrounding 10 to 30 whitish disk flowers. Many flower heads aggregate into flat-topped clusters located at the ends of branches.

Fruits and Seeds:

Single-seeded fruits are egg-shaped, about 1/10 inch long, flat, grayish, and have whitish edges. Unlike many other species of the Asteraceae, common yarrow seeds are not topped with a tuft of hairs (pappus).

Similar Species:

Common yarrow leaves and those of wild carrot (Daucus carota) appear similar except leaves of common yarrow are more feathery and finely dissected. Also, common yarrow has a perennial root system including creeping rhizomes whereas wild carrot is a biennial species with a large taproot.

Biology:

Plants flower from June until October. On average, plants produce 1600 seeds per year, and seeds are reported to be long-lived in the soil. Rhizomes spread 3 to 10 inches in a typical year, which would increase a 2-foot-square patch to four times its original area. Several cultivated forms are available for purchase as ornamental perennials. Common yarrow does not survive cultivation. Where frequently mowed, the plant persists in a low-growing form. Several herbicides are available that effectively control this weed.

Toxicity:

The plant contains compounds known to cause such allergic reactions as rashes, dermatitis, and eczema in some individuals. Common yarrow also contains the alkaloid achilleine, which reportedly promotes perspiration.

Facts and Folklore:

'Achillea' was the common name given to the plant by the Greeks in reference to Achilles, who used common yarrow to treat wounds incurred by his soldiers when they stormed Troy in 1200 B.C.; 'millefolium', which means 'thousand-leaved' or 'many-leaved', likely referred to the finely divided leaves. The common name 'yarrow' was derived from 'garawa', an old German name for the plant. 'Squirrel tail' was given as a common name because the feathery leaves emerge early in March.

Common yarrow was used to treat a variety of wounds and ailments. As recently as the 1940's, common yarrow leaves and flowers could be purchased for medicinal use from several American drug companies.